1. Field of the Invention
This invention relates to new alkyl norbornyl ether sulfonate compositions of matter. The invention also relates to a process for preparing the alkyl norbornyl ether sulfonates and to solutions containing such compositions. These solutions are useful for recovering petroleum in enhanced oil recovery processes.
2. Prior Art
Petroleum is normally recovered from subterranean formations in which it has accumulated by penetrating the formation with one or more wells and pumping or permitting the petroleum to flow to the surface through these wells. When this primary production is exhausted some form of supplemental or enhanced recovery process must be applied to the formation in order to extract petroleum.
Water flooding, which involves the injection of water into the subterranean, petroleum containing formation for the purpose of displacing petroleum toward the producing well, is the most economical and widely practiced supplemental recovery method. Water does not displace petroleum with high efficiency, however, since water and oil are immiscible, and also because the interfacial tension between water and oil is quite high. Persons skilled in the art of oil recovery have recognized this inherent weakness in water flooding and many additives have been described in the literature for decreasing the interfacial tension between the injected water and the formation petroleum. For example, U.S. Pat. No. 3,302,713 discloses the use of petroleum sulfonates prepared from a specific boiling range fraction of the petroleum feed stock for a surfactant in oil recovery operation. Other surfactants which have been proposed for oil recovery operations include alkylpyridinium salts, alkyl sulfates, alkylaryl sulfates, ethoxylated alkyl or alkylaryl sulfates, alkyl sulfonates, alkylaryl sulfonates and quaternary ammonium salts.
The above described surfactants are satisfactory in some formations, particularly where the salinity as well as concentration of divalent ions in the formation water is relatively low. Generally, the salinity must be less than about 1,000 parts per million and the concentration of divalent ions must be less than about 200 to about 500 parts per million in order to permit the use of the most commonly available primary anionic surfactants such as petroleum sulfonate.
Persons skilled in the art have recognized the limitation of simple anionic surfactants such as petroleum sulfonate and have described the use of certain solubilizing co-surfactants therewith. U.S. Pat. Nos. 3,811,504; 3,811,505; and 3,811,507 describe certain mixtures of alkyl or alkylaryl sulfonates and nonionic surfactants which exhibit satisfactory performance in petroleum formations having high salinity and/or hard water. U.S. Pat. No. 3,508,612 describes the use of a dual surfactant system comprising an organic sulfonate such as a petroleum sulfonate and a sulfated, ethoxylated primary or secondary alcohol, which is compatible with high salinity and/or high divalent ion containing formation waters. U.S. Pat. Nos. 3,827,497 and 3,890,239 relate to oil recovery fluids and processes which are compatible with high salinity formation waters and involve organic sulfonate and sulfonated, ethoxylated alcohol mixtures.
While the aforementioned multicomponent systems can be rendered soluble in high salinity and/or high divalent ion concentration formation waters, their use has not always been satisfactory because the ratio of the concentrations of the primary anionic surfactant and the solubilizing co-surfactant are extremely critical and vary with the salinity, divalent ion concentration, as well as with the specific surfactant composition being employed. If too little solubilizing surfactant is used, the primary anionic surfactant precipitates in the presence of the high salinity water. If too much solubilizing surfactant is used, the material is rendered so soluble in water that its effectiveness for purposes of reducing the interfacial tension between the drive water and the formation petroleum is greatly reduced. In either case, oil recovery falls off sharply. Moreover, the cost of the solubilizing co-surfactant is generally two to five times as great as the cost per pound of the primary anionic surfactant, and the use of excessive amounts of solubilizing co-surfactant renders an oil recovery process economically unattractive.
In view of the foregoing discussion, it can be appreciated that there is a substantial unfulfilled commercial need for an efficient and economical petroleum recovery method applicable to formations containing high salinity and/or high divalent ion concentration.